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Toxicological information

Skin sensitisation

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Administrative data

skin sensitisation: in vivo (LLNA)
Type of information:
experimental study
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guideline
according to guideline
OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)
- modification: in addition, measurements of ear swelling and ear weight were done to discriminate the irritating potential from the sensitizing potential of the test substance (Integrated Model for the Differentiation of Skin reactions (IMDS))
Principles of method if other than guideline:
Modified LLNA (IMDS; Integrated Model for the Differentiation of Skin Reactions). Modifications are authorised in the OECD TG 429 and in the Note for Guidance SWP/2145/00 of the CPMP (2001). Information on validation of IMDS and scientific justification is given in: Vohr HW et al., Arch. Toxicol., 73, 501-509 (2000); Ehling G et al., Toxicology 212, 60-68 and 69-79 (2005).
GLP compliance:
yes (incl. QA statement)
Type of study:
mouse local lymph node assay (LLNA)

Test material

Constituent 1
Chemical structure
Reference substance name:
2,2'-methylenediphenyl diisocyanate
EC Number:
EC Name:
2,2'-methylenediphenyl diisocyanate
Cas Number:
Molecular formula:
Details on test material:
- Name of test material (as cited in study report): MDI 22
- Physical state: solid
- Purity: approx. 100 % (as indicated by the sponsor)
- Lot/batch No.: WRS 3792
- Storage condition of test material: room temperature

In vivo test system

Test animals

Details on test animals and environmental conditions:
- Source: Charles River, Sulzfeld, Germany
- Strain: Crl:NMRI BR
- Age at study initiation: 7 weeks
- Weight at study initiation: 28 - 32 g
- Housing: individual
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: at least 6 days

- Temperature (°C): 22 +/- 2
- Humidity (%): 40 - 70
- Air changes (per hr): about 10
- Photoperiod (hrs dark / hrs light): 12 / 12

Study design: in vivo (LLNA)

acetone/olive oil (4:1 v/v)
0, 2, 10, 50 %
No. of animals per dose:
Details on study design:
The test item in the formulation, the positive control or the vehicle were applied epicutaneously onto the dorsal part of both ears of the animals. This  treatment was repeated on three consecutive days (d1, d2 and d3). The volume administered was 25µl/ear. The used concentrations were based on the experiences with the test system and the toxic properties of the test substance.
The animals were anaesthetized by inhalation of carbon dioxide and sacrificed one day after the last application (d4). The appropriate organs were then removed. Lymphatic organs (the auricular lymph nodes) were transferred into physiological saline (PBS).
- weight of draining lymph nodes (given as weight index compared to vehicle controls)
- cell counts in draining lymph nodes (given as cell count index compared to vehicle controls)
Stimulation indices were calculated by dividing the absolute weight or number of cell counts of the substance treated lymph nodes by the vehicle treated ones.
- ear swelling (given in 0.01 mm and as index)
- ear weight (given in mg/8 mm diameter punch and as index)
- body weights
Positive control substance(s):
hexyl cinnamic aldehyde (CAS No 101-86-0)
When it was statistically reasonable, the values from treated groups were compared with those from the control group by a one-way analysis of variance (ANOVA) when the variances are considered homogeneous according to a homogeneity testing like Cochran's test. Alternatively, if the variances are considered to be heterogenous (p<=0.05), a non-parametric Kruskal-Wallis test has been used (Kruskal-Wallis ANOVA) at significance levels of 5% . Two sided multiple test procedures were done according to Dunnett or Bonferroni-Holm, respectively. Outlying values in the LN weights were eliminated at a probability level of 99% by Nalimov's method. In addition, for the LLNA/IMDS the smallest significant differentes in the means were calculated by Scheffels method, which according to Sachs can be used for both equal and unequal sample sizes.

Results and discussion

Positive control results:
Alpha hexyl cinnamic aldehyde showed a clear sensitizing potential in the local lymph node assay (IMDS).

In vivo (LLNA)

Remarks on result:
other: see Remark
The results show  that the test item has a sensitizing potential in mice after dermal application. Compared to vehicle treated animals there was a clear increase in weights of the draining lymph nodes (indices of 2.90, 3.14 and 3.64 %, resp.) and in the cell counts (indices of 3.10, 2.60 and 3.00 %, resp.) at dose groups of 2, 10 and 50 %. These changes are of statistical significance. The "positive level", which is 1.4 for cell counts, has been exceeded in all dose groups.

Any other information on results incl. tables

Table 1: Summary of the LLNA/IMDS results with MDI 22 (means of 6 animals per group)

Parameter investigated




 2 %


10 %


50 %



Stimulation index:

weight of draining lymph nodes


2.90 *

3.14 *

3.64 *

1.85 *

Stimulation index:

cell count in draining lymph nodes


3.10 *

2.60 *

3.00 *

2.28 *

Ear swelling in 0.01 mm on day 4 (index)



 23.58 *


 23.83 *


 26.83 *


 21.42 *


Ear weight in mg / 8 mm diameter punch on day 4 (index)



 17.23 *


 17.82 *


 19.38 *


15.78 *



* statistically significant increase (p ≤ 0.05)

The "positive level" of ear swelling, which is 2 x l0-2 mm increase, has been exceeded in all dose groups. An increase in this parameter would point to an acute irritant (inflammatory) response. However, such an irritant property could also be combined with a strong skin sensitizing potential of a test compound. Nevertheless, it must be concluded that the test item has an irritant potential at all concentrations tested. Although it is not possible to calculate an exact EC value from the data obtained, it can be assumed that the EC value is in any case below 1%. In accordance with the classification proposed in the Technical Report No.78 of ECETOC this value corresponds to a strong skin sensitizer.

The body weights of the animals were not affected by any treatment.

Applicant's summary and conclusion

Interpretation of results:
Category 1 (skin sensitising) based on GHS criteria
harmonized classified in the European Union with H317 Category 1 Annex VI Regulation (EC) No 1272/2008 (CLP regulation)
Under the test conditions used 2,2’-MDI was skin sensitizing.
Executive summary:

MDI 22 (2,2'-MDI) was investigated in the modified local lymph node assay (LLNA-IMDS) on female mice according to OECD TG 429. Concentrations of 0 (vehicle control), 2, 10 and 50% formulated in acetone/olive oil (4:1) were tested. The results show that MDI 22 has a strong sensitizing potential in mice after dermal application. Compared to vehicle treated animals there was a significant increase regarding the weights of the draining lymph nodes and the cell counts in all dose groups. The corresponding cell count indices were 3.10, 2.60 and 3.00 exceeding the "positive level" of index 1.4. A significant increase compared to vehicle treated animals regarding ear swelling and ear weights was detected in all dose groups. An increase in this parameter would point to an acute irritant (inflammatory) response. However, such an irritant property can also be combined with a strong skin sensitizing potential of a test compound. However, there are indications that irritation can contribute to a mild unspecific stimulation of  lymphocyte proliferation (McGarry 2007*) which can lead to a bias in response indicating a strong sensitizing potential in  the LLNA.

2,2’-MDI is harmonized classified in the European Union with H317 Category 1 CLP Annex VI Regulation (EC) No 1272/2008 (CLP regulation).

*McGarry, H. F. (2007). The murine local lymph node assay: Regulatory and potency considerations under REACH. Toxicology 238:71-89.